Present study demonstrated that educational intervention was effective in improving nutrition knowledge, attitude, perceived behavioral control, and intention among school-going adolescents. Nutrition education is essential for encouraging healthy eating any strategy focused on changing behavior. Nutrition education in schools during early life is a key factor influencing students' eating behaviors [30] TPB was used as a theoretical framework in many studies on healthy diets and was found effective in increasing healthy eating intention among adolescents [20,25,27,31]. Another systematic review of the theory of planned behavior in behavior change intervention was conducted by Hardman et al [32]. They found that half of the educational interventions resulted in changed intentions, while two-thirds led to behavior change.
The findings of this study have demonstrated that the intervention package significantly increased the mean scores across all TPB constructs, knowledge and behaviour. Specifically, in the TPB constructs, the changes in mean scores from baseline to follow-up for knowledge (20.49), attitude (12.49), perceived behavioral control (16.16), and intention (14.88) regarding healthy eating showed a greater increase in the intervention group compared to the control group. The differences in baseline and follow-up scores within the intervention group were significant for all constructs, knowledge, behaviour except for BMI. This could be attributed to the short-term nature of the intervention and its focus on raising awareness and promoting healthy nutritional practices rather than inducing biological changes.
The changes observed in the control group might be due to the passage of time, whereas the differences in the intervention group likely result from both the time effect and the intervention itself. When examining the difference in mean scores, a positive change is evident in the intervention group for all constructs. Interestingly, the control group showed a slight negative difference in all constructs except for the knowledge score. This trend was also observed in a similar study carried out by Gharlipour et al., which examined 6th-grade students' breakfast eating habits [33]. A study by Dhauvadel et al. used extended TPB, which also included intention towards a healthy diet, added to a 1- and half-hour session delivered 2 consecutive days among grade nine students using similar methods, and done follow-up in 15 days. It also showed significant improvements (p<0.001) in all measured TPB constructs except subjective norms, while there was no significant change in the control group[34]. Another randomized controlled trial conducted. among 6th-grade students' breakfast eating habits used a 40-minute intervention in five sessions, based on TPB similar to the present study. It showed significant improvements in all TPB constructs except subjective norms in the follow-up than in baseline (p< 0.001) which this study did not measure. While that study conducted a two-month follow-up to observe behavior, our study focused on intentions towards healthy eating and short term behaviours, so our follow-up period was only four weeks after the intervention [33]. In this study, primary focus was on promoting healthy eating habits through small, manageable changes in daily activities that students easily adopted. This approach likely contributed to the positive impact observed across all TPB constructs.
Knowledge saw the most significant improvement, with an increase of over 20%. Acquiring knowledge is the first step toward transforming other constructs[35].This short-term knowledge gain, measured at a four-week follow-up, aligns with a systematic review that showed a 13% increase in nutrition knowledge in the intervention group compared to the control group[36]. Additionally, since the participants were students, they might have been exposed to other sources of information during the study period, which was beyond the researchers' control.
This study showed that the intervention strengthened the beliefs and attitudes of adolescent students, leading to a higher tendency to perform healthy eating behaviors. This may be because their perceived engaging in healthy eating behavior has more advantages than disadvantages. The present study demonstrated a positive shift in attitudes toward healthy eating in the intervention group compared to the control group. which is consistent with various studies based on TPB among students [33,37–41]. In another study among students with dietary behavior in India, intervention with 2 sessions of 1 hour each per class showed significantly increased attitude scores in 15 days (paired t-test I=-15.51, p<0.01, C=1.517, p=0.131) [42]. Inconsistent a study based on TPB regarding healthy diets among adolescents in India showed attitude, PBC, and intention score after the intervention were not significantly improved in 3 months This could be explained by several factors, including the lack of a direct intervention based on this construct, duration of intervention, and research methodology [27]. At the same time, other studies showed the changes in the perceived behavioural control and intention construct of TPB showed there were differences between intervention and control (p < 0:001)[43]. Another study also attitude and intention construct of TPB more remarkable than changes in the different constructs (p < 0:01) [34]
In the current study, there was no significant difference in BMI after the intervention in the group. These results align with another study [44]. This could be the short-term nature of the intervention and the intervention package's focus on awareness and promoting healthy nutritional practices rather than behavioral change.
The intervention significantly increased the intention for healthy eating in the intervention group compared to the control group (p<0.001). Notably, similar findings were observed in studies by [39,45,46], where intervention groups showed significantly higher intention scores for healthy eating compared to controls (p<0.001). Likewise, Tsorbatzoudis found that a TPB-based intervention, including posters and lectures promoting healthy eating, led to more positive intentions in the treatment group compared to the control group (p<0.001) [43].
The strength of this study is the use of TPB as the framework of this study, which is widely used for healthy diet intervention studies that could be used to increase healthy eating intentions among adolescents. Another strength was the educational approach, which was relatively simple, short-term, and contextualized in Nepalese setting, thus making it feasible to implement. Thirdly, this study used a quasi-experimental design with DID analysis, controlling the extraneous factors.
The study had some limitations: Firstly, it used a quasi-experimental design instead of a randomized controlled trial, potentially introducing selection bias. Secondly, dropout rates were notable. Thirdly, self-reported data might be influenced by social desirability bias. Lastly, the short duration of follow-up assessments underscores the need for longer-term studies.